1. Field of the Invention
The present invention relates to measuring the percentage of water in crude oil flow and, more particularly, relates to a method and apparatus for determining the instantaneous conductivity of crude oil flow at a given location in a conduit to determine the percentage of water contained therein.
2. Discussion of Art
"Water-cut" monitors frequently are attached to pipelines containing crude oil flow in order to determine the water content of the crude oil flow. In fact, most lease agreements require that this type of measurement be made. In addition, it is often desirable to determine the water content of the production actually flowing down in a bore hole.
One common form of a "water-cut" monitor is a capacitance-probe. The probe is actually inserted into the pipe to determine the dielectric constant of the crude oil as it flows through the pipe. Changes in a dielectric constant are related to the amount of water in the flow and, therefore, the output signal is representative of the amount of water contained in the flow. Although capacitance "water-cut" monitors provide accuracy and reliability, such devices are expensive.
Prior to the filing of this application, a search was conducted of issued patents relating to the field of the present invention. The patents uncovered are:
______________________________________ Inventor Reg. No. Issued ______________________________________ O. D. Jordan 2,752,586 June 26, 1956 F. C. Doble 2,807,956 Oct. 1, 1957 M. B. Mathews 2,913,893 Nov. 24, 1959 G. A. Marsh 3,192,473 June 29, 1965 R. H. Pfrehm 3,488,996 Jan. 13, 1970 E. N. Shawhan 3,515,988 June 2, 1970 Cirulis et al. 3,892,127 July 1, 1975 Perieres 3,899,688 Aug. 12, 1975 November 3,906,198 Sept. 16, 1975 Maxon 3,909,709 Sept. 30, 1975 Allender 4,030,028 June 14, 1977 Herzl 4,048,854 Sept. 20, 1977 Dowling et al. 4,059,987 Nov. 29, 1977 Ohtsu et al. 4,082,997 Apr. 4, 1978 Tassano 4,112,744 Sept. 12, 1978 Potter 4,116,045 Sept. 26, 1978 Ghahramani 4,225,778 Sept. 30, 1980 Reed et al. 4,236,406 Dec. 2, 1980 Cheney 4,251,809 Feb. 17, 1981 Thompson 4,266,188 May 5, 1981 Rosso 4,340,938 July 20, 1982 ______________________________________
The 1959 patent to Mathews sets forth a conductivity measuring device for use in dry-cleaning apparatuses which, as shown in FIGS. 3 through 7, utilizes electrical probes 39 and 40 longitudinally disclosed in a circular passageway for measuring the presence of water in a dry-cleaning solvent flowing therein. The 1975 patent to Maxon relates to an electrode 82 disposed in a circular passageway, as shown in FIG. 1 of Maxon, for measuring the conductivity of water in a gasoline mixture such as in a gas or fuel tank. The 1981 patent issued to Thompson discloses three probes for measuring the conductivity of a liquid in which they immerse such as in a pipe. The first probe is immersed in pure water, the second probe is immersed in pure oil, and the third probe is immersed in the actual flow. The 1977 Allender patent relates to a method and apparatus for detecting conductive particles in an oil flow system. The apparatus is placed in an areas of static oil flow and any metal particles in the oil flow will settle out and change the resistance of the circuit.
The remaining patents are not as close to the teachings of the present invention as those discussed above and pertain to other approaches such as: capacitance techniques (Rosso, Ghahramani, Tassano, Shawhan), specific gravity (Pfrehm), velocity of sound (Cirulis and Reed), heat of vaporization (Cheney), surface detection (Bronson and Ohtsu), volumetric ratios (Herzl), and optical detector (Perieres).
As the present invention relates primarily to "conductivity" water-cut probes, only the above discussed Mathews, Maxon, Thompson, and Allender patents are pertinent to the teachings of the present invention. As observed in the Mathews patent, the distribution of water in the flow (in the Mathews situation organic solvent) is not generally uniform over time. Furthermore, as found in Mathews et al, it is important that the conductivity electrodes not restrict the flow of fluids. Finally, it is noted in Mathews that the conductivity system operate continuously to measure the electrical conductivity of the fluid flow. As recognized in the Maxon patent, it is important that the electrical conductivity device not cause possible ignition of the flowing fluids. In addition, as also set forth in Maxon, the continuous application of current to the electrical probes can result in electrolysis thereby possibly rendering the device inaccurate and requiring frequent recalibration. The advantages of using a multiplexer to sample at rates of one to two hundred sets of measurements per second are set forth in the Thompson patent wherein three separate probes are inserted into the flowing fluid.
The present invention seeks to incorporate the advantages set forth above but, at the same time, improving upon the specifically discussed approaches. In particular, the present invention provides a three dimensional measurement of the amount of water in the crude oil flow by providing a number of instantaneous conductivity measurements at a plurality of locations in a plane located at angles substantially vertical to the flow of the fluids. Mathews, Maxon, and Thompson provide essentially a single instantaneous conductivity measurement in such a plane. The present invention utilizes a plurality of nodes all located in a plane substantially vertical or vertical to the flow of the fluids.